This is a rather weird-looking exercise, but it's a very effective way to build the whole deltoid with an emphasis on the lateral portion.
Basically, the movement is like performing a one-arm lateral raise while the other arm is brought up with the elbow bent at a 90 degree angle. The bent arm doesn't do much work because of the advantageous lever, but it allows you to keep some tension on the shoulder muscle during the whole exercise. Constant tension equals more growth!
We can always count on Christian to give us some great new movements that, in addition to spurring new muscle growth, will elicit bewildered stares from all the ACE certified trainers in the gym.
When anyone talks about training for any goal, they need to consider force, speed, and muscle fiber recruitment. They're the gears that are driving the bus, and Chad Waterbury is at the wheel. Remember, though, that the driver carries no change.